Two-cycle engine with an exhaust control device

Abstract: Object : To provide an exhaust control device for a two-cycle engine which does not impart a change of a shape of an exhaust passage. Constitution : An exhaust control device 15 provided in an exhaust port 7 opening to an inner peripheral surface of a cylinder hole 5 of a two-cycle engine 1, wherein a cylinder wall portion 17 adjacent to the exhaust port 7 is formed with a rotational face 21 obtained by rotating an arc having substantially the same curvature as the inner peripheral surface of the cylinder hole 5 about a rotational axis C₁ extending at a right angle to an axis C of said cylinder hole in the outside of said cylinder hole and a recess 16 defined by both ends at a right angle to the rotational axis C₁ and in communication with the.exhaust port 7; within said recess is mounted an exhaust passage member 18 having an exhaust passage 27 in communication with the exhaust port 7 and having an external shape substantially similar to said recess with a predetermined clearance formed relative to said recess in a portion above at least an upper edge 7a of the exhaust port 7 of said rotational face portion 21 and said both end portions; and a valve body 20 is provided which comprises arm portions 34 respectively inserted into the clearance in said both end portions and supported for swinging about the rotational axis C₁ and a control face portion 35 provided by connecting ends of said arm portions together and movable in and out of the clearance 28 in the rotational face portion 21 in response to the swinging of the arm portions 34.

Description: The present invention relates to a two-cycle engine comprising an exhaust control device provided in an exhaust port opening to an inner peripheral surface of a cylinder hole of the two-cycle engine. In a two-cycle engine in which an exhaust port and a scavenging port which are opened and closed by a piston are formed in an inner peripheral surface of a cylinder hole, fresh air compressed within a crank chamber is fed from the scavenging port into a cylinder chamber, and burnt gas is discharged out of the exhaust port, a "blow-by" occurs in which in an up stroke of the piston, a part of fresh air is discharged out of the exhaust port during a period from the closure of the scavenging port to the closure of the exhaust port. The procedure has been heretofore carried out in order to reduce the blow-by of fresh air such that an exhaust control valve is provided in an exhaust port so that when the engine is operated with a low load, the upper portion of the exhaust port is closed, and when the engine is operated with medium and high loads, the exhaust port is fully opened to change timing of opening and closing the exhaust port. Such known exhaust control valve comprises a rotary control valve in which a body portion is formed to be a substantially drum shape in the form of a recessed arc along the inner peripheral wall of the cylinder, and the surface of said body portion is positioned as close as possible to an exhaust port. The body surface of the control valve substantially functions as an upper edge of the exhaust port, and the body portion is scooped out so as to have substantially the same shape as the wall surface of the exhaust passage when the control valve is in a fully opened position. Japanese Patent Application Laid-Open Publication No. 23523/87 discloses an exhaust control valve in which said valve is provided above an exhaust passage extending outwardly from an exhaust port opening to an inner surface of a cylinder, and a control surface having substantially the same curvature as the inner surface of the cylinder and matching to the inner surface of the cylinder is provided at the swinging end of the valve body supported for swinging by a shaft disposed perpendicularly intersecting to the cylinder axis. In the upper portion of the exhaust passage is provided a recess in which the valve body is received when the exhaust port is fully opened. Further, EP-A-404 341, which corresponds to Japanese Patent Application Laid-Open Publication No. 33426/91 also discloses an exhaust control valve in which similarly to the former, a control surface (a flow shutoff cover) is provided at the swinging end of a valve body (main body) supported for swinging within an exhaust passage. In the just mentioned publication, the control surface is in the form of a flexible sheet, which is received into a slot-like cavity provided in the upper wall of the exhaust passage. In Figs. 7 and 8 of the aforementioned publication, there is shown an arrangement wherein a housing is provided within an exhaust passage, and said slot-like cavity is formed by a clearance between the outer surface of the upper wall of the housing and the inner surface of he upper wall of the exhaust passage. The housing is provided within the exhaust passage with both side walls thereof placed in contact with both side walls of the exhaust passage. The valve body for swinging the control surface is disposed internally of the exhaust passage along the inner surface of the housing side wall. In any of the aforementioned conventional exhaust control valves, a working member is positioned within the exhaust passage. Therefore, the sectional shape or the inner surface shape of the exhaust passage varies from a predetermined shape determined in terms of performance due to the presence of the working members and is varied by even the operation of the working members, which causes the lowering of output. It is an object of the invention to provide a two-cycle engine having an exhaust control device not lowering the output of the engine due to the operation of the control device. According to the present invention there is provided a two-cycle engine comprising: a cylinder block containing at least one cylinder hole provided with an exhaust port open to an inner peripheral surface of the cylinder hole, an exhaust passage member mounted on the cylinder block, the exhaust passage member being interiorly formed with an exhaust passage in communication with the exhaust port, an exhaust control device having a valve body varying the height of an upper edge of the exhaust port, the valve body being supported on a rotational shaft which extends at a right angle to a cylinder axis of the cylinder hole said valve body being formed by a thin shell-like member comprising an exhaust control portion substantially along a cylinder curvature in the exhaust port and at least swinging arm portion for connecting a side portion of the exhaust control portion and the rotational shaft, the exhaust passage member and a cylinder wall portion of the cylinder block forming a receiving chamber for receiving the valve body, the receiving chamber being communicated with the exhaust passage only in a working zone of the exhaust control portion of the valve body, characterized in that the receiving chamber receives the whole valve body in the fully open position of said valve body and, separated from the exhaust passage, provides a clearing receiving the swinging arm portion in every position of the valve body. Since the swinging arm portion of the valve body is always, that is in every working position of the valve body, received in the clearance of the receiving chamber associated thereto, the shape of the exhaust passage is not affected by the installation and operation of the valve body. Therefore, it is possible to prevent the output from being lowered. Furthermore, the valve body is formed from a thin shell-like member, and the exhaust control portion of the valve body can be moved up and down at a position sufficiently close to the exhaust port. Therefore, it is possible to precisely control an exhaust timing. The invention will be further described with reference to the drawings. In the drawings: Fig. 1 is a side view of a two-cycle engine provided with an exhaust control device according to the present invention with a cylinder portion thereof longitudinally sectioned. Fig. 2 is a side view of a cylinder portion showing the side opposite to that of Fig. 1; Fig. 3 is a sectional view taken along the line III-III of Fig. 1; Fig. 4 is an enlarged top view of a valve body; Fig. 5 is an enlarged side view of a valve body; Fig. 6 is a front view of a cylinder wall portion; Fig. 7 is a sectional view taken along the line VII-VII of Fig. 3; Fig. 8 is a front view of an exhaust passage member; Fig. 9 is a front view of a cover member and Fig. 10 is a rear view of a cover member. Fig. 1 is a side view of a two-cycle engine 1 provided with an exhaust control device according to the present invention, with a cylinder portion longitudinally section. Reference numeral 2 designates a crank case; 3 a cylinder block; and 4 a cylinder head. A scavenging port 6 and an exhaust port 7 are open to an inner peripheral surface of a cylinder hole 5 formed in the cylinder block 3 and opened and closed by a piston 8 which slidably moves up and down within the cylinder hole 5. Reference numeral 9 designates a connecting rod; and 10 a crank pin. At the time of up-stroke of the piston 6, fresh air is taken into the crank case 2 from an intake port 11. At the time of down-stroke of the piston 6, the fresh air is compressed and then fed into a cylinder chamber upwardly of the piston 6 via an intake passage 12 and the scavenging port 6. Burnt gas within the cylinder chamber is discharged out of the exhaust port 7. When the scavenging port 6 is closed and the exhaust port 7 is then closed by the upward movement of the piston 8, a mixed gas within the cylinder chamber is thereafter compressed by the piston 8 and fired by an ignition plug 14 adjacent to a combustion chamber 13. There occurs a "blow-by" wherein by the upward movement of the piston 8, a part of fresh air fed into the cylinder chamber is discharged out of the exhaust port 7 during a period from the closure of the scavenging port 6 to the closure of the exhaust port 7. This blow-by is great at the time of operation under low load (low rotation) at which the speed of the piston is slow. Therefore, at the time of the low-load operation, the upper portion of the exhaust port 7 is closed to quicken its closing timing, and an exhaust control device 15 is provided on the cylinder block 3 formed with the exhaust port 7 in order to lessen the blow-by of fresh air. The exhaust control device 15 is composed of a cylinder wall portion 17 formed with a recess 16, an exhaust passage member 18 mounted within the recess 16, a cover member 19 for covering the cylinder wall portion 17 and the exhaust passage member 18 from the outside, and a valve body 20 inserted in a receiving chamber between the recess 16 and the exhaust passage member 18. In the longitudinal section of Fig. 1, the recess 16 formed in the cylinder wall 17 is semicircular in shape having a radius r 1 in contact with an inner peripheral surface of the cylinder hole 5 about a point P. As will be understood from the cross section of Fig. 3, the radius r within the other longitudinal section parallel with the longitudinal section of Fig. 1 gradually increases to radii r 2 on both sides along an axis C 1 at a right angle to an axis C of the cylinder hole 5 passing the point P, and a line continuous to the outer ends of these radii r forms an arc a having substantially the same curvature as the cross sectional shape of the cylinder hole 5. That is, the face portion shown in Fig. 1 of the recess 16 is a rotational face obtained by rotating the arc a having substantially the same curvature as the inner peripheral surface of the cylinder hole 5 about the axis C 1 . Hereinafter, the face portion is called the rotational face portion 21, and the axis C 1 is called the rotational axis. The rotational face portion 21 is connected to end portions 22 and 22 each having a plane at a right angle to the axis C 1 at both ends in the direction of the rotational axis C 1 . That is, the recess 16 is defined by the rotational face portion 21 and the end portions 22 and 22 and is opened outwardly. Fig. 6 is a front view of the cylinder wall portion 17 formed with the recess 16 as described. The cylinder wall portion 17 has flat mating faces 23 on both sides with the recess 16 sandwiched therebetween, and is communicated with the exhaust port 7 in the central portion thereof. The exhaust passage member 18 mounted within the recess 16 has a contour substantially similar to the recess 16. That is, the exhaust passage member 18 comprises a rotational face portion 21a along the rotational face portion 21, end portions 22a and 22a along the end portions 22 and 22, and an outer end 24 (see Fig. 8) having the same surface as the mating surface 23 of the cylinder wall portion 17 along the open surface of the recess 16 (see Fig. 8). The exhaust passage member 18 is secured through a bolt 26 to the cover member 19 which is secured through a bolt 25 to the cylinder wall portion 17 as shown in Fig. 1, and thus is fixed with respect to the cylinder wall portion 17 and encased in the recess 16. The exhaust passage member 18 is interiorly formed with an exhaust passage 27 in communication with the exhaust port 7. Between the rotational face portion 21 of the recess 16 and the rotational face portion 21a of the exhaust passage member 18 is provided a clearance 28 having a predetermined spacing above an upper edge 7a of the exhaust port 7. The clearance 28 extends to a position slightly beyond a lower edge 7b of the exhaust port 7 (Fig. 1). Further, also between each end portion 22 of the recess 16 and each end portion 22a of the exhaust passage member 18 is provided a clearance 29 having a predetermined spacing (Fig. 3). The clearences 28 and 29 form the receiving chamber mentioned above for receiving the valve body 20. Fig. 9 is an external view of a cover member 19, and Fig. 10 is a rear view thereof. The back surface of the cover member 19 has a flat mating surface 30 having the same surface as the mating face 23 of the cylinder wall portion 17 and the outer end 24 of the exhaust passage member 18. The mating face 30 is placed in abutting contact with the mating face 23 and the outer end 24, and the cover member 19 is secured to the cylinder wall portion 17 and the exhaust passage member 18 by means of bolts 25 and 26 as previously mentioned. The cover member 19 is formed with an exhaust passage 27a continuous to the exhaust passage 27 of the exhaust passage member 18, and the exhaust port 7 is connected to an external exhaust pipe not shown through these exhaust passages 27 and 27a. The mating face 23 (Fig. 6) of the cylinder wall portion 17 and the mating face (Fig. 10) of the cover member 19 are respectively formed with a pair of bearing boss portions 31a and 31b which are opposed from both sides along the rotational axis C 1 . When the cylinder wall portion 17, the exhaust passage member 18 and the cover member 19 were assembled, a pair of bearing bosses 32 are formed, as shown in Fig. 3, by these bearing boss portions 31a and 31b. A valve body driving shaft (a rotational shaft) is rotatably supported on the bearing bosses 32. Fig. 4 is an enlarged top view of a valve body 20, and Fig. 5 is an enlarged side view thereof. As will be further understood from these figures, the valve body 20 is a thin shell-like member formed from a plate processed article, for example, such as a stainless steel plate, and is provided with a pair of arm portions (swinging arm portions) 34, and a control face portion (an exhaust control portion) 35 for connecting ends of these arm portions 34 together. The arm portion 34 is provided at it base end with a flat engaging hole 36. The arm portion 34 is inserted into a clearance 29 formed between the recess 16 and the end portions 22a of the exhaust passage member 18 with the engaging hole 36 engaged with a portion chamferred into a similar shape of the vaive body driving shaft 33. Accordingly, the arm portion 34 oscillates integral with the valve body driving shaft 33 within the clearance 29. The control face portion 35 is formed to be wider than the whole width of the exhaust port 7 and molded into a rotational surface having the same shape as the aforementioned rotational surface with respect to the rotational face portion 21 of the recess 16. When the arm portion 34 oscillates about the rotational axis C 1 integral with the valve body driving shaft 33, the control face portion 35 is accordinly free moved in and out of the clearance 28 between the rotational face portions 21 and 21a. Accordingly, the exhaust timing can be adjusted in accordance with the operating conditions by completely encasing the control face portion 35 into the clearance 28 to fully open the exhaust port 7 or projecting the control face portion 35 from the upper edge 7a of the exhaust port 7 to close the upper portion of the exhaust port 7. As will be understood from the foregoing, in the present embodiment, the recess 16 and the exhaust passage member 18 confine a receiving chamber for receiving the whole valve body 20. The receiving chamber is communicated with the exhaust passage 27 only in the working zone of the control face portion (exhaust control portion) 35, and the arm portion (swinging arm portion) 34 is always received in the clearance 29 of the receiving chamber. Since the clearance 28 extends to a position beyond the lower edge 7b of the exhaust port 7, the control face portion 35 can be moved down to said position to fully close the exhaust port 7. This configuration can be advantageously applied, for example, to the case where the loss of heat caused by exhaust is impeded at a certain period of cycle to promote natural firing of a mixture within the cylinder chamber so that a good combustion state is maintained along with the ignition by way of an ignition plug 14. One valve body driving shaft 33 is projected externally from the cylinder block 3. For driving this valve body driving shaft 33 a driving lever 37 is fixedly mounted. The driving lever projects to opposite sides of said shaft. Fig. 2 is a side view showing the side where the driving lever 37 for the driving shaft 33 is disposed. As shown in the figure, a servomotor 38 is mounted on said side. A driving cable 40 is passed over a pulley 39 provided on an output shaft of the servomotor 38, and both ends of the driving cable 40 are connected to both ends of the driving lever 37. Accordingly, the opening and closing operation of the exhaust port by the control face portion 35 of the valve body 20 is controlled by the servomotor 38. In the exhaust control device 15 thus configured, the arm portion 34 of the valve body 20 is not positioned interiorly of the exhaust passage 27 but disposed externally of the exhaust passage member 18 formed with the exhaust passage 27. Therefore, the shape of the exhaust passage 27 is not changed to bring forth the lowering of output by the provision of the valve body 20 and the operation thereof. Further, since the exhaust control portion 35 of the valve body 20 is moved up and down at a position sufficiently close to the exhaust port 7, it is possible to precisely control the exhaust timing. In addition, the exhaust port 7 can be fully closed as previously mentioned. The exhaust control device 15 constituted by the cylinder wall portion 17, the exhaust passage member 18, the cover member 19 and the valve body 20 is wholly cooled by cooling water which circulates through various portions. A cooling water circulating system within the exhaust control device 15 will be described hereinafter. First, the cylinder wall portion 17 is provided with a cooling water passage 41 2 in communication with a cooling water passage 41 1 provided on the cylinder block 3 encircling the cylinder hole 5 (Figs. 1 and 3). This cooling water passage 41 2 is disposed so as to surround the recess 16 from the bottom toward the both sides thereof as shown in Fig. 7 and is communicated with connecting ports 42 1 and 42 1 which are open to the lower portions on both the sides of the mating face 23 of the recess 16. Cooling water is introduced into the cooling water passages 41 1 and 41 2 through a cooling water inlet 43 (Fig. 7). The connecting port 42 2 registered with the connecting port 42 1 is provided in the mating face 30 of the cover member 19 in contact with the mating face 23 of the recess 16 (Fig. 10), and the cover member 19 is interiorly formed with a cooling water passage 41 3 in communication with the connecting port 42 2 . This cooling water passage 41 3 is opened to the mating face 30 through the opening portion 44 1 . The mating face 30 is also provided with other connecting ports 42 3 on upper both sides, and a cooling water passage 41 4 in communication therewith is opened to the mating face 30 through the opening portion 44 2 adjacent to the opening portion 44 1 . The opening portion 44 1 is separated from the opening portion 44 2 by a diaphragm 45. The exhaust passage member 18 is further provided with a cooling water passage 41 5 which is opened to the outer end 24 through the opening portion 44 3 as shown in Figs. 1 and 8. This cooling water passage 41 5 is in the form of a bag which communicates with the exterior only at the opening portion 44 3 . The opening portion 44 3 is matched to the opening portions 44 1 and 44 2 of the cover member 19. The cooling water supplied from the cooling water inlet 43 to the cylinder block 3 flows into the cooling water passage 41 5 via the cooling water passage 41 2 , the connecting ports 42 1 , 42 2 , the cooling water passage 41 3 , and the opening portions 44 1 , 44 3 , and after this, again passes through the opening portion 44 3 from the cooling water passage 41 5 . The cooling water then enters into the cooling water passage 41 4 through the opening portion 44 2 , during a period of which the cylinder wall portion 17, the cover member 19 and the exhaust passage member 18 are cooled thereby. The connecting port 42 3 of the cover member 19 is matched to the other connecting port 42 4 (Fig. 6) which is opened to the mating face 23 of the exhaust port 7. The aforesaid cooling water enters into the other cooling water passage (not shown) provided in the cylinder wall portion 17 through the connecting port 42 4 from the connecting port 42 3 and thence is guided to a cooling water passage 41 6 (Fig. 1) provided in the cylinder head 4 to cool the cylinder head 4, after which the cooling water is discharged out of the cooling water outlet 46. According to the present invention, the swinging arm portion of the valve body is separated from the exhaust passage and disposed externally thereof, and the shape of the exhaust passage is not affected by the provision of the valve body and operation thereof. Therefore, the lowering of output caused by the change of the shape of the exhaust passage can be prevented. Moreover, since the exhaust control portion of the valve body can be moved up and down at a position sufficiently close to the exhaust port, the exhaust timing can be precisely controlled. Furthermore, the exhaust port can be fully closed by the exhaust control portion.

Claims: Two-cycle engine comprising: a cylinder block (3) containing at least one cylinder hole (5) provided with an exhaust port (7) open to an inner peripheral surface of the cylinder hole (5), an exhaust passage member (18) mounted on the cylinder block (3), the exhaust passage member (18) being interiorly formed with an exhaust passage (27) in communication with the exhaust port (7), an exhaust control device (15) having a valve body (20) varying the height of an upper edge (7a) of the exhaust port (7), the valve body (20) being supported on a rotational shaft (33) which extends at a right angle to a cylinder axis (C) of the cylinder hole (5), said valve body (20) being formed by a thin shell-like member comprising an exhaust control portion (35) substantially along a cylinder curvature in the exhaust port (7) and at least one swinging arm portion (34) for connecting a side portion of the exhaust control portion (35) and the rotational shaft (33), the exhaust passage member (18) and a cylinder wall portion (17) of the cylinder block (3) forming a receiving chamber (28, 29) for receiving the valve body (20), the receiving chamber (28, 29) being communicated with the exhaust passage (27) only in a working zone of the exhaust control portion (35) of the valve body (20), characterized in that the receiving chamber (28, 29) receives the whole valve body (20) in the fully open position of said valve body (20) and, separated from the exhaust passage (27), provides a clearance (29) receiving the swinging arm portion (34) in every position of the valve body (20).

Inventors: ASAI MASAHIRO, ISHIBASHI YOICI, ISOMURA SHINICHI, KUDOU OSAMU, ASAI, MASAHIRO, ISHIBASHI, YOICI, ISOMURA, SHINICHI, KUDOU, OSAMU
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: F02D13
IPC codes: F02B75, F02D13